I've never dismantled an air bag, but I'd guess it's a screw in fitting with a brass thread one end and the push in fitting the other. the screw in end is probably either 1/4" or 1/8" BSP, in which case these are under £2 on ebay!! If this is the case and you're unsure which size it is, £4 isn't too much to buy n' try. It's worth noting that the size references don't actually refer to the straight diameter of the fitting, 1/8 BSP is approx. 9.7mm diameter and 1/4 BSP is about 13.1mm. Of course if the whole thing is moulded into the air bag you're stuffed! and you're looking at another bag.